Hypodermic syringe

ABSTRACT

A hypodermic syringe includes an elongate housing having rear and forward ends and a piston chamber which slidably supports the piston to define an innoculant storage space within the housing, a hollow needle supported by the plunger assembly and in communication with the storage space. The needle is extendable from the forward end of the housing and retractable into the housing during an injection stroke and a safety device is provided for preventing re-use of the syringe after completion of the injection stroke. The safety device includes an override chamber at the rear end of the housing and adjoining the piston chamber, the override chamber having a greater width than the piston chamber, and a displaceable diaphragm located at or adjacent the juncture of the piston and the override chambers to partition and seal the override chamber from the piston chamber, the diaphragm being displaced by the piston and the piston entering the override chamber at the end of the injection stroke.

FIELD OF THE INVENTION

This invention relates to a hypodermic syringe, and in particular to ahypodermic syringe having a retractable needle. This invention isapplicable for medical and veterinary applications, and it will beconvenient to hereinafter describe the invention in relation to thatexemplary application. However, it is to be appreciated that theinvention is not limited to those applications.

DESCRIPTION OF THE RELATED ART

Following the international concern on the spread of the A.I.D.S. virus,it is now realised that one major form of transmission of this virus isthrough contact with or use of syringes that have been infected with theA.I.D.S. virus.

In conventional hypodermic syringes, the needle remains exposed afteruse of that syringe. There is therefore the possibility of beingaccidentally pricked by the needle after the syringe has been used. Thismay result in infection with the A.I.D.S. virus if the patient is acarrier of that virus. Furthermore, the disposal of used syringes can bea hazardous procedure because of the exposed needles and the possibilitythat any one of the syringes may be infected.

Another disadvantage of conventional hypodermic syringes is that thesyringe can be readily re-used. In the case of intravenous drug users, asingle syringe is often shared by a number of people. This greatlyincreases the possibility of contracting the A.I.D.S. virus. If one ofthe persons is a carrier of the virus and infects the syringe, thissyringe will infect the others with the virus.

Syringes have been developed where the needle can be retracted after thesyringe has been used. Examples of such syringes are disclosed inAustralian Patent Application Nos. 13088/88, 14189/88 and 16234/88.These prior syringes are generally arranged in the same way asconventional syringes with a hollow needle extending from one end of acylindrical housing and a plunger assembly extending from the other endof the housing for displacing a piston supported therein. Means may beprovided on the piston to engage an end of the needle at the end of theinjection stroke. The needle can then be withdrawn by pulling the pistonback through the housing. Alternatively, the needle is supported onmeans which allow the needle to be withdrawn after the injection stroke.

In these prior arrangements, the needle remains exposed at the end ofthe injection until the retracting means are actuated. There istherefore still a possibility of accidental contact with the needleimmediately after the syringe has been used. Also, because the plungerassembly must be pulled back after the injection or the needle supportmust be actuated to retract the needle, the user may neglect to or haveinsufficient time to retract the needle so that it remains exposed aftersyringe use thereby negating the benefit of the retracting means.

It is therefore an object of the present invention to provide ahypodermic syringe having a hypodermic needle which can be retractedduring the injection stroke of the syringe to minimise the possibilityof accidental contact with the needle.

It is also a preferred object of the present invention to provide asingle use hypodermic syringe which cannot be or is difficult to re-use.

SUMMARY OF THE INVENTION

With this in mind, the present invention provides a hypodermic syringefor the injection of an inoculant liquid including a housing, a plungerassembly slidably supported by the housing, and a hollow needle whichcan be fully accommodated within and be extendible from the housingwherein the needle is supported by the plunger assembly and retractsinto the housing during an injection stroke of the syringe.

As the needle retracts into the housing during the injection stroke,there is no need for a further actuation of the syringe to retract theneedle.

The hypodermic syringe preferably further includes safety means fortrapping the needle within the housing after the completion of theinjection stroke. The plunger assembly preferably includes an elongatestem having a piston at one end thereof, the needle extending from theopposing end thereof and having a longitudinal needle passage incommunication with a longitudinal stem passage passing completelythrough the stem and the piston.

The housing preferably includes an elongate main body portion having acylindrical chamber therein for slidably supporting the piston, anelongate safety shroud portion having a forward tip and a needle chambertherein for accommodating the needle, and a needle bore passing throughthe forward tip of the safety shroud portion from the needle chamber.

The safety means previously referred to may include a shoulder providedadjacent the needle bore and within the needle chamber for trapping thetip of the needle when the needle is completely withdrawn from theneedle bore into the needle chamber, the needle moving out of alignmentwith the needle bore when not constrained therein. The longitudinal axisof the needle may be offset at an angle from the longitudinal axis ofthe stem when the needle is not constrained.

The safety means also or alternatively include an override chamberwithin the main body portion at a terminal end of the housing, theoverride chamber adjoining and having a greater width than the diameterof the cylindrical chamber for accommodating the piston after thecompletion of the injection. A displaceable diaphragm may be provided ator adjacent the juncture of the cylindrical and override chambers forpartitioning and sealing the override chamber from the cylindricalchamber, the diaphragm being displaced by the piston as it enters theoverride chamber. The diaphragm may have an interference fit within theoverride chamber, a shallow undercut being preferably provided in thewall of the override chamber to assist in locating and holding thediaphragm in position. The piston may also have a projection extendingtherefrom and towards the diaphragm, the projection being locatedadjacent to or near the periphery of the piston and being used tofacilitate the dislodgment of the diaphragm.

At least one outwardly extending barb may also be provided adjacent thepiston for preventing movement of the piston back into the cylindricalchamber after the piston enters the override chamber.

A needle cap may be integrally formed with and separable from theforward tip of the safety shroud portion, the forward tip having afrangible weakened portion adjacent to the needle cap whereby the needlecap can be twisted and separated from the forward tip to expose theportion of the needle held therein.

The plunger assembly preferably includes at least one handle memberextending laterally from the stem at or adjacent the opposing endthereof, an elongate longitudinal slot being provided in the housing toallow the or each handle member to extend out from the housing. Aperipheral wall preferably extends along at least a substantial portionof the periphery of the or each longitudinal slot.

The following description refers in more detail to the various featuresof the hypodermic syringe of the present invention. To facilitate anunderstanding of the invention, reference is made in the description tothe accompanying drawings where the hypodermic syringe is illustrated inpreferred embodiments. It is to be understood that the hypodermicsyringe of the present invention is not limited to the preferredembodiments as illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a longitudinal cross-sectional view of a first preferredembodiment of the hypodermic syringe of the present invention;

FIG. 1B is a longitudinal cross-sectional view taken through Section 1Bof FIG. 1A;

FIG. 1C is an exploded view of the hypodermic needle of FIGS. 1A and 1B;

FIG. 2A is a longitudinal cross-sectional view of the hypodermic syringeof FIGS. 1A and 1B showing the needle fully extended prior to injection;

FIG. 2B is a longitudinal cross-sectional view taken through Section 2Bof FIG. 2A;

FIG. 2C is a longitudinal cross-sectional view of the hypodermic syringeof FIGS. 1A and 1B showing the needle fully retracted after completionof injection;

FIG. 3 is a perspective view of the hypodermic syringe of FIGS. 1A and1B showing a preferred way to hold the syringe during the injection;

FIG. 4A is a longitudinal partial cross-sectional view of a secondpreferred embodiment of the hypodermic syringe of the present invention;and

FIG. 4B is a longitudinal view taken through Section 4B of FIG. 4A.

Referring initially to FIGS. 1A to 3, there is shown a first preferredembodiment of the hypodermic syringe of the present invention. Thehypodermic syringe includes a housing 1, a plunger assembly 2 slidablysupported within housing 1, and a hypodermic or hollow needle 3 integralwith an extending from plunger assembly 2. Plunger assembly 2 and needle3 move together as a single assembly. FIGS. 1A and 1B show thehypodermic syringe as supplied prior to use with needle 3 retractedwithin housing 1. It is also envisaged that the syringe be supplied withneedle 3 extended and with the syringe preloaded with inoculant liquid.

Housing 1 may be elongate and may have a main body portion 6 providingan elongate chamber 7 therein. The lateral cross-section of chamber 7may be circular to provide a cylindrical chamber. Non-circular lateralcross-sections for chamber 7 are also envisaged. From one end of mainbody portion 6 extends a safety shroud 8 having a needle chamber 9therein for accommodating needle 3. Cylindrical chamber 7 and needlechamber 9 are in communication to provide a single elongate andcontinuous chamber for accommodating the integral plunger assembly 2 andneedle 3. Safety shroud 8 and main body portion 6 are joined together toprovide elongate housing 1 of the syringe. In a preferred form, mainbody portion 6 may be substantially cylindrical in shape with safetyshroud 8 being tapered to provide a forward tip 10 of housing 1. Needle3 extends from forward tip 10 when the syringe is used.

Plunger assembly 2 may have an elongate stem 11, a piston 12 at one endof stem 11 and a handle means 13 at or near the opposing end of stem 11.The longitudinal axis of stem 11 is preferably at least substantiallyparallel to the longitudinal axis of housing 1 when plunger assembly 2is supported by housing 1. These longitudinal axes may also besubstantially aligned. Needle 3 preferably extends from the opposing endof stem 11. The longitudinal axis of needle 3 and stem 11 may be atleast substantially aligned when the syringe is in use. Alternativelylongitudinal axis of needle 3 may be offset at an angle to thelongitudinal axis of stem 11. A longitudinal stem passage 14 passingcompletely through stem 11 may be provided. Hypodermic needle 3 has alongitudinal passage passing completely therethrough to allow passage ofinoculant liquid. Stem passage 14 may be in communication with thelongitudinal needle passage to thereby provide a continuous passagethrough stem 11 and needle 3.

Handle means 13 may include at least one member extending at leastsubstantially laterally from stem 11 relative to its longitudinal axis.Preferably two such handle members 13 are provided extending laterallyin opposing directions from stem 11. Each handle member 13 may forexample be a simple lateral arm or may have a curved and flattened shapeto provide finger rests as shown in the drawings. Handle member 13 mayalternatively have an aperture to allow a finger to be passedtherethrough.

A longitudinal slot 15 may be provided in the wall of safety shroud 8for each handle member 13 to enable handle members 13 to extendexternally from housing 1. This enables the longitudinal displacement ofplunger assembly 2 and needle 3 to be controlled from outside thesyringe housing 1. The length of slot 15 may be sufficient to allowneedle 3 to be fully extended or fully contracted, the handle members 13preferably abutting the peripheral ends of slot 15 at either of theabove needle positions. A peripheral wall 16 may extend along at least asubstantial portion of the periphery of each slot 15. The provision ofwall 16 makes it more difficult to manipulate needle 3 when it is fullyretracted within safety shroud 8. To make the syringe even more tamperresistant, handle members 13 may be formed with a relatively thinsection so that slot 15 can be made very narrow thereby restrictingaccess to needle 3. To ensure that the thinner handle members 13 are ofsufficient strength, they may be made of a high strength, low weightmaterial such as magnesium metal. The complete plunger assembly 2 may bemade of this material.

Reinforcement means may be provided on stem 11 to increase its rigidityso as to prevent bending of stem 11 during use of the syringe. Thereinforcement means may also assist in guiding plunger assembly 2 withinhousing 1.

The reinforcement means may for example include at least one web 17extending from stem 11. Each web 17 may extend laterally from stem 11and longitudinally therealong. Preferably four of these webs 17 canextend equidistantly about stem 11 such that each web 17 is displaced90° about stem 11 from an adjacent web 11. Alternatively, just twoopposing webs 17 may be provided as shown in the drawings. Web(s) 17 maypreferably be integrally joined to handle members 13, stem 11 and piston12 to ensure that plunger assembly 2 moves as a single unit and toprevent or minimise deflection of stem 11, handle members 13 or piston12 from their correct operating positions.

Piston 12 may be slidably accommodated within, cylindrical chamber 7 andin sealing engagement with the wall of that chamber 7. Piston 12 mayhave a piston face 18 extending at least substantially laterallyrelative to the longitudinal axis of stem 11 with stem passage 14 havingan inlet/outlet opening 31 in piston face 18. Cylindrical chamber 7 mayhave a terminal end opposing piston 12 which is preferably closed off sothat cylindrical chamber 7 and piston 12 can define a liquid holdingspace 23 (as shown in FIGS. 2A and B) in which the inoculant liquid tobe injected can be held prior to injection. The terminal end may beprovided by an end wall closing off cylindrical chamber 7 or may beprovided by a displaceable sealing diaphragm 26 as shown in thedrawings. Liquid holding space 23 may therefore be defined bycylindrical chamber 7, piston face 18 and diaphragm 26.

Needle 3, when fully retracted, can be accommodated within needlechamber 9 of safety shroud 8. A needle bore 19 may extend from needlechamber 9 through forward tip 10 of housing 1 to allow needle 3 toextend out of housing 1. Needle 3 may be extended by forwardlydisplacing the handle member(s) 13 towards forward tip 10 of housing 1to the position as illustrated in FIGS. 2A and B. This will displaceplunger assembly 2 towards forward tip 10, resulting in needle 3extending through needle bore 19 and out of housing 1. The forwardmovement of plunger assembly 2 also displaces piston 12 away fromdiaphragm 26 thereby increasing the volume of liquid holding space 23.To retract needle 3, handle members 13 are rearwardly displaced awayfrom forward tip 10 which results in the displacement of plungerassembly 2 away from forward tip 10 retracts needle 3 back into safetyshroud 8 and displaces piston 12 towards diaphragm 26 reducing thevolume of liquid storage space 23.

Prior to use of the syringe, needle tip 4 may be accommodated withinneedle bore 19 in forward tip 10. Needle bore 19 may terminate within aseparate needle cap 5 which may be releasably secured to forward tip 10.Alternatively, needle cap 5 may be formed as an integral part of safetyshroud 8 as shown in the illustrated embodiment. Forward tip 10 may beprovided with opposing twist tabs 20 extending laterally therefrom. Itis also envisaged that a plurality of ribs be provided on the outersurface of needle cap 5 to enable it to be securely gripped by thefingers. A weakened frangible area may be provided in forward tip 10adjacent twist tabs 20. This may simply be provided by an annular groove21 encircling forward tip 10.

Using twist tabs 20, needle cap 5 can be twisted off forward tip 10 toexpose needle tip 4, needle cap 5 breaking away from the remainder offorward tip 10 at annular groove 21. This arrangement helps to preventcontamination of needle 3 prior to the actual use of the syringe. Italso provides a visual indication that the syringe has been used orotherwise tampered with.

It is also envisaged that a nozzle seal may simply be provided to coverthe exit opening of needle bore 19. The seal may preferably be formedintegrally with forward tip 10. Needle tip 4 must initially breakthrough the seal before the syringe can be used. The seal shouldtherefore be relatively thin to allow it to be pierced by the needle. Tobreak through the seal, plunger assembly 2 must be forwardly displacedso that needle 3 can penetrate through the seal.

After a small portion of needle 3 is exposed with the removal of needlecap 5, the needle tip 4 may be inserted into a bottle of inoculantliquid for drawing the required dose. As needle 3 is extended furtherfrom housing 1, the volume of liquid storage space 23 within the syringeincreases inducing a vacuum which can draw the inoculant liquid upthrough needle 3 and through stem passage 14 to storage space 23. Needle3 may be extended until the syringe is fully charged with liquid or whenthe correct dosage of liquid is held therein.

The liquid may then be injected by displacing housing 1 towards thepoint of penetration of needle 3. This may be accomplished with one handas shown in FIG. 3 by engaging one or more fingers with the handlemembers 13 extending from housing 1 and resting the palm or the thumb ofthe hand on the rear end of housing 1. By pressing the rear end ofhousing 1 with the palm or thumb towards handle members 13, liquidstorage space 23 is made to decrease in volume thereby forcing theliquid out through stem passage 14 and needle 3 to the injection area.During the injection stroke, needle 3 is progressively retracted backinto housing 1.

Needle 1 preferably retracts completely into housing 1 at the end of theinjection and safety means may be provided to prevent or make itdifficult for the syringe to be used again. This safety means mayinclude a shoulder 22 immediately adjacent to needle bore 19. Shoulder22 may form the forward end of needle chamber 9 behind needle bore 19.Whereas needle bore 19 preferably has a diameter which provides minimalclearance between bore 19 and needle 3 when held therein, needle chamber9 is relatively wider than bore 19 so that shoulder 22 is providedbehind needle bore 19.

Needle tip 4 can be trapped by shoulder 22 when needle 3 is fullyretracted within needle chamber 9. To facilitate the trapping of needletip 4, needle 3 may move out of alignment with needle bore 19 when notconstrained therein.

In one arrangement, needle 3 may be provided with an "offset bias"wherein the longitudinal axis of needle 3 normally deviates at an anglefrom the longitudinal axis of stem 11 when needle 3 is not constrained.The bias angle may be relatively small e.g. about 1.0 degrees. Whenplunger assembly 2 is supported within cylindrical chamber 7, thelongitudinal axis of stem 11 may be parallel to and aligned with thelongitudinal axis of needle bore 19 before and during use of thesyringe. As needle 3 is supported by and constrained by needle bore 19,the longitudinal axis of needle 3 is initially aligned with thelongitudinal axis of needle bore 19. Needle 3 is therefore deflectedagainst its offset bias resulting in a spring tension being maintainedin needle 3 before and during use of the syringe. If needle 3 isretracted completely back into needle chamber 9, needle tip 4 can beextracted from needle bore 19 so that needle 3 is no longer constrainedby bore 19. Because of the offset bias, needle 3 will realign itselfaway from the longitudinal axis of bore 19 so that needle tip 4 movesaway from alignment with needle bore 19 and is caught within needlechamber 9 behind shoulder 22. If there is an attempt to extend needle 3again, needle tip 4 will engage shoulder 22 preventing extension ofneedle 3. Attempts to force needle 3 forward may lead to needle tip 4being at least partially imbedded in shoulder 22.

In an alternative arrangement, the longitudinal axis of needle bore 19may be laterally offset from the longitudinal axis of stem 11. Needle 3does not then need to be provided with an offset bias because the offsetposition of needle bore 19 will deflect needle 3 when supported therein.The resultant spring tension in needle 3 will ensure that realignmentoccurs when needle 3 is extracted from needle bore 19.

A further safety means may be provided to prevent or make it difficultfor someone using the syringe to intentionally leave out a small portionof needle 3 after injection enabling re-use of the syringe. To providethis safety means, main body portion 6 may include an override chamber24 at the terminal end of main body portion 6. Override chamber 24 maybe cylindrical, may be in communication with and have a wider diameterthan cylindrical chamber 7 and may have a longitudinal axis aligned withthe longitudinal axis of main cylindrical chamber 7. A substantiallyannular shoulder or wall 25 may therefore be provided betweencylindrical chamber 7 and override chamber 24. The terminal end ofhousing 1 may be sealed by an end cap 28 thereby closing off the openend of override chamber 24.

Diaphragm 26 may abut or be adjacent to annular shoulder 25 to partitionand seal override chamber 24 from cylindrical chamber 7. In onearrangement, diaphragm 26 may have an interference fit within overridechamber 24 in the position as shown in the illustrated embodiments.Frictional forces between the periphery of diaphragm 26 and the wall ofoverride chamber 24 hold diaphragm 26 in position. It is also envisagedthat a shallow undercut (not shown) be provided in the wall of overridechamber 24 adjacent annular shoulder 25 to accommodate the periphery ofdiaphragm 26 so as to assist in locating and holding diaphragm 26therein. Alternatively, diaphragm 26 may be supported by a resilientmeans which presses diaphragm 26 against annular shoulder 25. Theresilient means may for example be a spring although other resilientmeans are also envisaged.

Piston 12 may have a peripheral wall 27 in sealing engagement with thewall of cylindrical chamber 7 when the syringe is in use. Peripheralwall 27 may be chamfered to provide a frusto-conical wall surface. Thediameter of piston 12 preferably increases towards piston face 18. Atleast peripheral wall 27 of piston 12 is preferably resilient so thatpiston 12 is compressed when supported within cylindrical chamber 7 tomaintain sealing engagement therein. Alternatively, peripheral wall 27may have an annular groove for accommodating a separate sealing meanssuch as an O-ring to maintain piston 12 in sealing engagement withcylindrical chamber 7.

Prior to use of the syringe with needle tip 4 initially supported inneedle bore 19, piston 12 is located immediately adjacent to or abutsdiaphragm 26 as shown in FIG. 1A. In the arrangement where diaphragm 26is supported by resilient means, it is envisaged that piston 12 can atleast partially depress diaphragm 26 into override chamber 24. As needle3 is extended, piston 12 moves up cylindrical chamber 7 to the positionshown in FIGS. 2A and B.

During the injection stroke, piston 12 moves back towards diaphragm 26.At the end of the injection stroke as shown in FIG. 2C, piston 12presses and displaces diaphragm 26. To assist in dislodging diaphragm 26when it is interference fitted within override chamber 24, a projection29 may be provided on piston face 18. Projection 29 may extend at leastsubstantially normal to and away from piston face 18 towards diaphragm26, and may be located near or adjacent to the periphery of piston face18. The pressing force provided by the retracting plunger assembly 2 isconcentrated at the point where projection 29 engages diaphragm 26. Thispoint is near the periphery of diaphragm 26 so that only a relativelysmall force is required to dislodge diaphragm 26 at its peripheral edgecompared with the force that would be required if diaphragm 26 waspressed at its centre. The end of the injection can be clearly feltbecause of the drop in the resistance to the movement of handle members13 felt by the user as diaphragm 26 is displaced. The displacement ofdiaphragm 26 results in the loss of compression within cylindricalchamber 7 disabling the syringe. Furthermore, as piston 12 entersoverride chamber 24, needle 3 may also be totally withdrawn from needlebore 19 into needle chamber 9 to trap needle 3 behind shoulder 22.

In certain situations, it is preferable for the syringe to beconstructed so that it is difficult for the user to know when the end ofthe injection occurs. This prevents, for example, an intravenous druguser from controlling the use of the syringe so that needle 3 remainspractically extended at the end of the injection thereby allowing re-useof the syringe by another person. In the arrangement describedpreviously, where diaphragm 26 is supported by resilient means, it isdifficult for the syringe user to know when piston 12 reaches thispoint. This is because diaphragm 26 can be readily displaced by piston12 and there is no definite "stop" for plunger assembly 2 to show thatthe inoculant liquid has been fully injected by the syringe. It willtherefore be difficult for the user to avoid the complete retraction ofpiston 12 beyond cylindrical chamber 7 and into override chamber 24 andthe complete retraction of needle 3 within needle chamber 9.

Because the diameter of override chamber 24 is larger than cylindricalchamber 7, piston 12 can expand from its compressed state as it enterschamber extension 24. The chamfered peripheral wall 27 also assists inguiding piston 12 into override chamber 24. This is because as piston 12reaches annular shoulder 25, the expansion of piston 12 and the shape ofchamfered peripheral wall 27 of piston 12 acts to "pull" piston 12 intooverride chamber 24. This rearward pulling effect further ensures thatit is difficult to prevent the full retraction of needle 3 after use ofthe syringe.

To further ensure that piston 12 remains trapped in override chamber 24,at least one projection or barb 30 may be provided on the face of thepiston 12 directed towards needle 3 or may extend from each web 17adjacent piston 12. Barbs 30 may be resilient and may extendsubstantially laterally and beyond peripheral wall 27 of piston 12 asshown in FIG. 1C when piston 12 is not constrained within cylindricalchamber 7. As shown in FIG. 1A, barbs 30 are initially deflected towardsstem 11 when piston 12 is supported within cylindrical chamber 7. Whenpiston 12 enters override chamber 24, barbs 30 expand laterallyoutwardly. Barbs 30 will engage annular wall 25 if there is an attemptto pull piston 12 back into cylindrical chamber 7.

The hypodermic syringe of FIGS. 1A to 3 may be used in the followingmanner:

(a) The syringe is supplied with needle 3 enclosed within safety shroud8 to prevent contact and therefore contamination of needle 3.

(b) Needle cap 5 is twisted off to expose needle tip 4. For example,about 6 mm of needle 3 is exposed for the purposes of drawing inoculantliquid. The removal of needle cap 5 also provides an indication that thesyringe has been used or tampered with.

(c) An inoculant liquid is drawn into liquid holding space 23 by movinghandle members 13 towards forward tip 10 thereby exposing needle 3, toits full working length in readiness for injection. Having drawn insufficient liquid, piston 12 may be activated into compression to removeany air in the normal manner.

(d) As the inoculation into the patient is proceeding, safety shroud 8advances down needle 3 to a position where forward tip 10 touches theflesh at the conclusion of the injection movement. As diaphragm 26 mustbe displaced, a distinct resistance is felt at the conclusion of theinjection delivery stroke so that the user is made aware that the dosehas been administered.

(e) By continuing the compression stroke, the syringe is disabled as theabove noted resistance is felt and the syringe is rendered useless andsafe. Needle 3 is totally withdrawn within safety shroud 8 andcompression in cylindrical chamber 7 is lost. In this way there is noway of touching needle 3 because it is shrouded as it leaves thepatient's flesh.

A second preferred embodiment of the present invention is shown in FIGS.4A and 4B. This embodiment is adapted for use in deep muscularinoculation but is otherwise identical to the first embodiment.

In the first embodiment needle 3 is progressively withdrawn into housing1 during inoculation so that only needle tip 4 remains exposed at theend of the inoculation and just prior to needle 3 being fully withdrawninto housing 1 by the safety means described above. It is therefore notsuitable for deep muscle inoculation where the syringe must penetratedeeply through a fat layer into the muscle. To adapt the presentinvention to this application, the second embodiment provides anelongate needle cap 105 to allow a greater length of needle 103 to beinitially exposed when needle cap 105 is removed. Needle cap 105 mayalsoo have twist tabs 1120 and may be integrally formed with safetyshroud 108 with a frangible area in the form of an annular groove 121 inthe wall of safety shroud 108 as in the first embodiment.

Needle 103 can therefore penetrate more deeply as a greater lengthremains exposed at the end of the innoculation and prior to fullretraction of needle 103. Because needle 103 would be relatively longerthan needle 3 of the first embodiment, the main body portion 106 wouldalso need to be longer than main body portion 6 of the first embodimentto enable the longer needle 103 to be accommodated within housing 101.In particular, the override chamber (not shown) of main body portion 106would need to be long enough to allow plunger assembly 102 to be fullyretracted. To facilitate the use of this embodiment of the syringe,handle members 113 may be elongated in the longitudinal directiontowards end cap 128 to enable the fingers to readily reach handlemembers 113.

Housing 1, 101 may be produced in two sections to facilitate theinsertion of plunger assembly 2, 102 and needle 3, 103 therein. Forexample the safety shroud 8, 108 may be produced separately from themain body portion 6, 106. Plunger assembly 2, 102 may then be insertedinto main body portion 6, 106 before safety shroud 8, 108 is securedthereon to form the complete housing 1, 101. Diaphragm 26 and anyresilient means may be inserted through the open end of override chamber24. End cap 28, 128 may then retain the above components therein.

In an alternative arrangement, housing 1, 101 could be produced as anintegral unit with plunger assembly 2, 102 inserted into housing 1through side slot 15, 115 in safety shroud 8, 108 or through the openend of main body portion 6, 106.

The various components of the syringe can be readily manufactured usingconventional injection moulding methods and can be typically made ofplastic materials. For example, the main body portion 6, 106 and safetyshroud portion 8, 108 can be moulded from high impact polystyrene,piston assembly 2, 102 and end cap 28, 128 can be moulded frompolypropelene and diaphragm 26 moulded from ABS.

The syringe of the present invention may be supplied within a containerto prevent premature actuation of the safety means of the syringe. Aspreviously noted, it is also envisaged that the syringe be suppliedpreloaded with a dose of inoculant liquid. As the needle will already beextended to its full working length from the syringe housing, anelongate needle cap is required to accommodate the extended needle. Thesyringe would be otherwise identical to the above described embodiments.

The hypodermic syringe of the present invention is much more safer touse and to dispose of because the needle is totally withdrawn into thehousing at the end of the injection stroke of the syringe. There is noneed to subsequently actuate a needle retracting means after theinjection stroke eliminating the possibility of the needle remainingexposed after syringe use. Furthermore, the hypodermic syringe of thepresent invention can preferably only be used once thereby ensuring thata contaminated syringe cannot be re-used.

It should be appreciated that various modifications and additions may bemade to the hypodermic syringe without departing from the ambit of theinvention defined in the claims appended hereto.

I claim:
 1. A hypodermic syringe including an elongate housing having rear and forward ends and a piston chamber therein, a plunger assembly having a piston, the piston chamber slidably supporting the piston to define an inoculant fluid storage space within the housing, a hollow needle supported by the plunger assembly and in communication with the storage space, the needle being extendable from the forward end of the housing and retractable into the housing during an injection stroke of the syringe wherein safety means are provided for preventing re-use of the syringe after the completion of the injection stroke, wherein the safety means includes an override chamber at the rear end of the housing adjoining the piston chamber and having a greater width than the piston chamber, and a displaceable diaphragm located at or adjacent the juncture of the piston and override chambers to partition and seal the override chamber from the piston chamber, the diaphragm being displaced by the piston as the piston enters the override chamber at the end of the injection stroke.
 2. A hypodermic syringe including an elongate housing having a main body portion and a safety shroud portion adjoining the main body portion, a piston chamber provided within the main body portion, a plunger assembly having a piston, the piston chamber slidably supporting the piston to define an inoculant fluid storage space within the main body portion, a hollow needle supported by the plunger assembly and in communication with the storage space, the safety shroud portion having a forward tip and a needle chamber therein for accommodating the needle, a needle bore passing through the forward tip of the safety shroud portion from the needle chamber through which the needle can extend, the needle retracting into the safety shroud during an injection stroke of the syringe, wherein safety means are provided for preventing re-use of the syringe after the completion of the injection stroke, wherein the safety means includes an override chamber at the rear end of the main body portion adjoining the piston chamber and having a greater width than the piston chamber, and a displaceable diaphragm located at or adjacent the juncture of the piston and override chambers to partition and seal the override chamber from the piston chamber, the diaphragm being displaced by the piston as the piston enters the override chamber at the end of the injection stroke, the safety means further including a shoulder provided adjacent the needle bore within the needle chamber for trapping the tip of the needle when the needle is completely withdrawn from the needle bore into the needle chamber, the needle moving out of alignment with the needle bore when not constrained therein.
 3. A hypodermic syringe according to claim 1 or 2 wherein the diaphragm has an interference fit within the override chamber, and a shallow undercut is provided in the wall of the override chamber to assist in locating and holding the diaphragm in position.
 4. A hypodermic syringe according to claim 3 wherein the piston has a projection extending therefrom and towards the diaphragm, the projection being located adjacent to or near the periphery of the piston and being used to facilitate the dislodgment of the diaphragm.
 5. A hypodermic syringe according to claim 3 wherein at least one outwardly extending barb is provided on the plunger assembly adjacent the piston for preventing movement of the piston back into the cylindrical chamber after the piston enters the override chamber.
 6. A hypodermic syringe according to the claim 1 further including an elongate safety shroud portion adjoining the main body section and having a forward tip and a needle chamber therein for accommodating the needle, and a needle bore passing through the forward tip of the safety shroud portion from the needle chamber, through which the needle extends.
 7. A hypodermic syringe according to claim 6 wherein the safety means further includes a shoulder provided adjacent the needle bore and within the needle chamber for trapping the tip of the needle when the needle is completely withdrawn from the needle bore into the needle chamber, the needle moving out of alignment with the needle bore when not constrained therein.
 8. A hypodermic syringe according to claim 6 or 2 wherein a needle cap is integrally formed with and separable from the forward tip of the safety shroud portion, the forward tip having a frangible weakened portion adjacent to the needle cap whereby the needle cap can be twisted and separated from the forward tip to expose the portion of the needle held therein.
 9. A hypodermic needle according to claim 6 or 2 wherein the plunger assembly includes an elongate stem having the piston at one end thereof, and at least one handle member extending laterally from the stem at or adjacent the opposing end thereof.
 10. A hypodermic syringe according to claim 9 wherein at least one elongate longitudinal slot is provided in the housing to allow the or each handle member to extend out from the housing.
 11. A hypodermic syringe according to claim 10 wherein a peripheral wall extends along at least a substantial portion of the periphery of the or each longitudinal slot.
 12. A hypodermic needle according to claim 9 wherein the needle communicates with the inoculant fluid storage space by way of a passage passing through the plunger assembly. 